The present disclosure generally relates to electrochemical cells. More particularly, the present disclosure relates to electrochemical cells, such as molten salt electrochemical cells (e.g., molten sodium metal chloride), having a mechanism for reducing the possibility of an overfill or overpressure condition during a charging operation of the electrochemical cells.
During a charging operation of an electrochemical cell, such as a molten salt electrochemical cell, an electrolyte (e.g., beta alumina solid electrolyte), which separates the anodic chamber from the cathodic chamber fills a space within the electrochemical cell. During a charging operation, metal ions dissociate from the molten salt (e.g., sodium ions dissociate from sodium chloride salt). The metal ions from the molten salt are conducted through the electrolyte structure and get deposited in the anode as a molten liquid metal charging medium, the possibility exists that the electrolyte may become overfilled (e.g., filled beyond a recommended level) with this charging medium. In such an overfill condition, the electrochemical cell is at risk of failure due to the possibility of an increased pressure in the anode space enclosed/separated by the electrolyte, which may rupture the electrolyte structure in the electrochemical cell.
In a battery (i.e., a plurality of electrochemical cells in electrical contact with one another) there is a potential that during a charging operation one or more of the anodes in the electrochemical cells may fill with a molten liquid metal charging medium (e.g., sodium in sodium metal chloride batteries) more rapidly than others. For example, better performing electrochemical cells of the battery may fill more rapidly than lesser performing cells during the charging operation. Thus, the possibility exists that the electrochemical cells of the battery will not evenly fill with the charging medium during the charging operation. In such a situation, the better performing cells (i.e., the more rapidly filling electrochemical cells) are at risk of an overfill condition before the lesser performing cells.
Ordinary batteries, and methods of charging, are not configured to prevent the overfill condition of better performing cells while maintaining the charging operation of the lesser performing cells. If the charging operation is not halted, the electrochemical cells in the overfill condition may rupture and/or fail. Thus, ordinary batteries may be undercharged if a charging operation of the battery is halted to prevent the better performing cells from being in an overfill condition.
Alternatively, ordinary batteries may include a connection by which the charging medium is transferred from an overfilling cell to another of the cells during a charging operation of the battery. However, such a design requires that the electrolyte of the cells be in fluid communication with one another (i.e., the cells are not individually sealed), to allow for the overfilling electrolyte to flow the charging medium from one cell to another.
The present disclosure provides an apparatus, method and charging system incorporating, for example, an electrochemical cell including a mechanism for reducing or eliminating the possibility of an overfill or overpressure condition, without requiring that the electrolytes of the electrochemical cells be in fluid contact with one another.